1. Carpy, A., Galy, J.: Acta Chem. Scand. 25 (1971) 1918.
2. Brusset, H., Gillier-Pandraud, H., Voliotis, S.D.: Mater. Res. Bull. 6 (1971) 5.
3. Labbe, Ph., Frey, M., Allais, G.: Acta Cryst. B29 (1973) 2204.
4. Fesenko, E.G., Gavrilyachenko, V.G., Martynenko, M.A., Semenchev, A.F., Lapin, I.P.: Kristallografiya 18 (1973) 1014; Soviet Phys.-Cryst. (English Transl.) 18 (1974) 635.
5. Giess, E.A., Scott, B.A., Burns, G., O'Kane, D.F., Segmüller, A.: J. Am. Ceram. Soc. 52 (1969) 276.